CURLOPT\_HTTPSIG\_KEYID(3) Library Functions Manual CURLOPT\_HTTPSIG\_KEYID(3)

# [NAME](#NAME)

CURLOPT\_HTTPSIG\_KEYID - key identifier for HTTP Message Signatures

# [SYNOPSIS](#SYNOPSIS)

```
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HTTPSIG_KEYID, char *keyid);
```

# [DESCRIPTION](#DESCRIPTION)

This feature is **experimental** and may change before it is considered stable. We advise against using it in production.

Pass a null-terminated string that identifies the key used for RFC 9421 HTTP Message Signatures. This value is included as the *keyid* parameter in the *Signature-Input* header, allowing the server to look up the corresponding verification key.

The application does not have to keep the string around after setting this option.

Using this option multiple times makes the last set string override the previous ones. Set it to NULL to disable its use again.

# [DEFAULT](#DEFAULT)

NULL

# [PROTOCOLS](#PROTOCOLS)

This functionality affects http only

# [EXAMPLE](#EXAMPLE)

```
int main(void)
{


  CURL *curl = curl_easy_init();


  if(curl) {


    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/api");


    curl_easy_setopt(curl, CURLOPT_HTTPSIG_ALGORITHM, CURLHTTPSIG_ED25519);


    curl_easy_setopt(curl, CURLOPT_HTTPSIG_KEY,


                     "9f8362f87a484a954e6e740c5b4c0e84"


                     "229139a20aa8ab56ff66586f6a7d29c5");


    curl_easy_setopt(curl, CURLOPT_HTTPSIG_KEYID, "my-key-id");


    curl_easy_perform(curl);


  }
}
```

# [AVAILABILITY](#AVAILABILITY)

Added in curl 8.22.0

# [RETURN VALUE](#RETURN_VALUE)

[*curl\_easy\_setopt(3)*](/man/os/curl/curl_easy_setopt.3) returns a CURLcode indicating success or error.

CURLE\_OK (0) means everything was OK, non-zero means an error occurred, see [*libcurl-errors(3)*](/man/os/curl/libcurl-errors.3).

# [SEE ALSO](#SEE_ALSO)

[**CURLOPT\_HTTPSIG\_ALGORITHM**(3)](/man/os/curl/CURLOPT_HTTPSIG_ALGORITHM.3), [**CURLOPT\_HTTPSIG\_KEY**(3)](/man/os/curl/CURLOPT_HTTPSIG_KEY.3)

2026-10-31 libcurl

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Document: CURLOPT_HTTPSIG_KEYID(3) from curl 8.23.0-r3 (Chainguard OS)
Source: https://github.com/curl/curl.git